Based on the observation data of MICAPS, this paper analyzed the strong temperature drop in the Inner Mongolia Reach during 20-23November, 2016. The results show that the strong temperature drop leading to the rapid freeze-up of the river is closely related to the verticaltrough in the vicinity of the Beihu Lake. There is a high pressure ridge development over 500hPa from the Caspian Sea to the West Siberian Plain,of which the ridge collapse is the forecast key of the vertical and strong cold air to the south. With the high-altitude transverse trough to the verticalsouth, the small high-pressure split out of the ground cold high-pressure constantly moving southward and influence the Inner Mongolia River.The cold troughs in the lower reaches of Inner Mongolia have been intensified during the course of the movement, and the strong cold advectionoccurred under the northerly winds, which aggravated the temperature gradients in the Inner Mongolia Reach and resulted in the strong cold airweather. When a large number of cold air accumulated in the northern lowlands of Siberia, and a typical weather situation activated, forecastersshould consider that the Inner Mongolia will have strong cooling process. At the same time, if the river flow is small, with each station along theriver dropped by a cold wave standard in 48h, and the biggest drop is beyond 14℃, forecasters should consider that the Inner Mongolia will quicklychange from the ice flow to freeze up.